Nuclear energy reactors



July 31, 1962 H- POLAK NUCLEAR ENERGY REACTORS Original Filed July 6,1956 Ffg/ SAS

lOl

INVENTOR Herm PoZcz/ BY M, [L6/l @Mal/,2

orneys July 31, 1962 H. PoLAK 3,047,483

NUCLEAR ENERGY REACTORS Original Filed July 6, 1956 7 Sheets-Sheet 2 fFI6 FIC? 7 M Tf L fllo FICTMO L INI/ENTOR. w lov Hehrz POZQ/ `Iuly 31,1962 H. PoLAK 3,047,483

NUCLEAR ENERGY REAcToRs Original Filed July 6, 1956 '7 Sheets-Sheet 3FI@ I] COOLANT F LOW INVENTOR. Henri polczk Attorneys July 3'1, 1962 1|`POLAK 37,047,483

NUCLEAR ENERGY REACTORS Original Filed July 6, 1956 7 Sheets-Sheet 4FR?. f3 FIC?. M

FUEL

m 57m/Crum L E COOLA/vr INVENToR. Henn Pola/ k ttorneys July 31, 1.962H. POLAK 3,047,483

NUCLEAR ENERGY REAcToRs original Filed July e, 1956 7 sheets-sheet 5INVENTOR. He hrz pola 7 July 31, 1962 H. POLAK NUCLEAR ENERGY REAcToRsoriginal Filed July 6. 1956 7 Sheets-Sheet 6 A uri.'

INVENToR. Henn 0o Zal BY /QW" Stes 5 Claims. (Cl. 2M-193.2)

This invention deals `with the internal structure of nuclear reactors,the invention being useful both in reactors of the type utilizingthermal neutrons and of the so-called fast-neutron type. y 4

In both types of reactors, nuclear energy is released in a chainreaction wherein neutrons freed as the result of nuclear iissions in thefuel substance are employed to .produce iissions of other atoms' of thefuel. Maintenance of the chain reaction requires good neutrol economy inthe reaction zone, `which means that that zone should be left relativelyfree of substances tending to absorb free neutrons. Removal of thegenerated heat of reaction, which oonstitutes the principal usefulenergy output of the reactor, requires, on the other hand, that somesuitable heatexcnange medium be circulated through or around thereaction zone.

The energy output of the reactor is limited in large measure by thespeed and efiiciency With which the heat of reaction can be removed. Thebest coolants are liquids, but` unfortunately in many cases thematerials which make good coolants are also poisonous to the nuclearreaction, that is, they absorb free neutrons and hence tend to inhibitthe chain reaction. This is particularly true of thermal-neutronreactors.

In most prior-art reactors, therefore, a compromise has had to be struckbetween favorable neutron economy and effective heat removal andutilization.

One method of achieving heat removal without introducingneutron-absorbing materials into the reaction zone is to use nuclearfuel prepared in liquid form and circulate it between the reaction zoneand an outside heat exchanger. This method is frequently referred to asexternal cooling. It has its practical difficulties, however,particularly in the pumping of very hot, highly radioactive liquids,which is not easy to do on a continuous basis.

The major object of the present invention is to provide a reactor inwhich the fuel itself provides the means of heat transfer from thereaction zone to the cooling zone, without any of the problemsencountered when the fuel is prepared as a free, relatively unconnedliquid. This object is achieved in my invention by designing thefuelbearing elements in suitable shape yand then rotating themsystematically so that each portion of the fuel passes alternatelythrough the reaction zone and through a cooling zone. By shaping thefuel elements to possess substantially axial symmetry, I achievecontinuous energy release and heat transfer yat a constant rate, eventhough each differential volume of fuel is passing alternately betweenreaction conditions and cooling conditions.

In a preferred form of my invention for thermal reactors, a rotary fuelassembly is employed, consisting of a number of parallel disc-shapedcircular fuel-bearing plates mounted on a shaft rotated at a constantrate, `whereby said fuel plates successively move through a regionsubstantially filled with a suitable moderator, and another regionlargely filled with coolant, the geometric and nuclear parameters -beingselected in such manner that the self-supporting chain reaction issubstantially confined to the `moderating region. The fission heatgeneratedv within the fuel discs by the chain reaction is mechanicallyremoved into the cooling zone by the rotation of the discs themselves.

In addition to an outer reliector or blanket, surrounding both thechain-reacting and cooling regions, an internal separator or internalreflector may be situated around the vreacting zone (the so-called innercore), slots being provided therein to accommodate the individual fueldiscs and permit their rotation. Preferably the geometry of theconstruction is so chosen that the cooling phase for' any given volumeof fuel lasts longer than the reaction phase. Such design improves theefficiency of heat transfer.

In my invention a `coolant with high mass number, and therefore poorslowing-down power, is not only permissible, but often even desirable,since the use of such a coolant will improve the effectiveness of theinterruption of the chain reaction in the cooling zone.

In the case of fast reactors, and in particular fast breeders, thedesign considerations are somewhat different from those in thermalreactors, with the result that my invention is best employed withanother type of core arrangement. In such reactors, however, myinvention, employing rotary fuel-bearing assemblies, offers greatadvantages over prior-art designs.

In breeder reactors, any degradation of the neutron spectrum results inan increase of the oapture-to-ssion ratio. Furthermore, the fast-fissionbonus contributed by the fertile material reaches attractive proportionsat high neutron energies. Therefore it is highly desirable to avoidappreciable slowing down of the neutrons in both inelastic and elasticcollisions.

In `any fast-neutron reactor the fuLl should contain a large proportionof fissionable material with the lowest possible dilution bynon-iissionable atoms, other than fertile atoms in a breeder reactor. Asa result of this `design requirement, the core of a fast reactor isusually small, providing a small heat transfer area and thus makingspeedy removal of heat by a coolant particularly difficult.

Thus in practice the power of a fast reactor is limited by the possiblerate of .heat removal. The doubling time in a fast breeder reactor beinginversely proportional to thespecic power, such a reactor will bepreferably run at the maximum permissible power levels, and it is,therefore, of essential importance that the heat removal rate be raisedto its possible maximum.

Since the flux land power generation generally show a strong maximum inthe central region of the core, relatively more heat has to be removedfrom this region than from the surrounding zone. If this is achieved byan increase of the coolant proportion within the centra-l zone, anadditional factor lof dilution is introduced, which softens the neutronspectrum. Thus generally a compromise between central core specic powerand fastneutron energy level must be made.

Another major object of the present invention is to provide afast-neutron reactor in which such a compromise in design is avoided.According to my invention, removal of heat from the high power-densityregion of the core is accomplished by the use of two interlocking setsof rotating disc-shaped fuel elements. The heat of fission developedwithin them, in the main reactive zone of mutual overlap, is removedmechanically, by the disc rotation, from this inner core into adjoiningcooling zones which encompass the outer portions of the discs. In thisway the inner core region remains essentially undiluted with coolant,except for small quantities in the clearances between adjoining discs.

The outer core area or cooling zone, on the other hand, is not onlygreatly diluted by coolant, but also contains many fewer fissile atomsper unit volume than the inner region. Hence the neutron flux and powergeneration Will remain largely restricted to the inner zone which thediscs of fuel overlap.

A n internal separating reflector may, if desired, be locatedimmediately around the zone of overlap, slots being provided toaccommodate the rotating fuel discs, as previously described withrespect to the thermal reactor form of my invention.

The temperature distribution along the two fuelcontaining plateassemblies Will be essentially flat, in contrast with the distributionof heat produced, which will show a marked maximum in the inner corewhere the discs overlap. The coolant should preferably not, by acting asa moderator, contribute noticeably to the overall reactivity, and itshould, therefore, have a high mass number. It may, moreover, containpart or all of the fertile material, in cases wherein the reactor isbeing used for breeding as well as energy production. The geometry ofthe system as just described provides, for any given volume segment ofthe fuel discs, a considerably longer cooling period than reactingperiod during each rotation. This will, of course, facilitate heattransfer.

In both thermal and fast reactors constructed according to my invention,the fuel itself may, during operation, be in the form of liquid metal oralloy encapsulated within hollow disc-shaped fuel-containing elementshaving temperature-resistant structural walls, the fuel being held inthe outer portions of the discs by the centrifugal force caused byrotation. Mounting of the fuel assembly shafts in a vertical positionand providing a slight internal taper in the disc walls make possiblethe lling and emptying of the discs with liquid fuel merely by raisingor lowering the overall fuel level in a system of communicating vessels.If excess fuel in the center shaft is drained off during operation, thefuel discs will empty themselves into the center shaft region as soon astheir rotation is interrupted or slowed down.

This constitutes an important feature of self-quenching in cases offailure of rotation. Hence another object of my invention is to providean added factor of safety in nuclear reactors.

Quite apart from the above-mentioned advantages of rotating fuel discassemblies for the physical separation of chain reaction and coolingfunctions, these assemblies offer two distinct additional advantages, tobe considered as further objects of this invention.

In the first place, it is possible to let the rotary fuel assemblyfurnish part or all of the pumping power necessary to propel the primarycoolant through its circuit at the required rate. This can either beeffected by mere utilization of the tangential drag forces of the fueldiscs upon the coolant, or by employing the radial centrifugal forceswhich act upon the coolant as it is whirled around by the rotatingdiscs.

In the second place, when liquid metallic fuel is carried in rotary fueldiscs, the centrifugal forces will tend to separate the relatively lightssion products from the heavier fissile and fertile atoms, and thefission products will accumulate close to the axis of rotation. Thismakes possible continuous withdrawal of fission products during reactoroperation, a very important practical advantage. At the same time thisconstruction, by keeping ssion product contamination at all times low,permits a design having less excess reactivity, and the inherent safetyof the reactor is correspondingly increased.

The objects above described and furthei advantages obtainable with thisinvention are explained and illustrated for the appended drawings andthe following detailed discussion of the illustrative embodiments of theinvention therein disclosed.

This application is a continuation of application S.N. 596,326, filedJuly 6, 1956, now abandoned.

The various gures of the drawing may be briey described as follows:

FIGURE l is a diagrammatic cross section of a core assembly for athermal-neutron reactor with separated reacting and cooling regions,according to the invention.

FIGURE 2 is a diagrammatic cross section of the FIG- URE l structure,the section being along the line 2 2 of FIGURE 1.

FIGURE 3 shows the shading code used in FIGURES 1-10.

FIGURE 4 is diagrammatic sectional view showing typical relativedimensions of the fuel element, coolant and moderator geometry withinthe inner core of the FIGURE 1 reactor, and FIGURE 5 is a similar viewshowing typical geometry in the cooling region of the reactor of FIGURE1.

FIGURE 6 gives qualitative curves for the temperature of a specificelement of a fuel disc of the reactor of FIG- URE l, as it rotates at aconstant rate in a steady-state condition.

FIGURE 7 shows a qualitative curve of energy gain or loss of a specificsmall portion of a fuel disc of the reactor of FIGURE l, as it rotatesat a constant rate in a steady-state condition.

FIGURE S is a diagrammatic flow diagram of a thermal-neutron reactormade according to the teaching of FIGURE 1, in which the circulation ofliquid coolant is aided by the tangential drag-pumping effect of therotary fuel discs.

FIGURE 9 is a diagrammatic tlow diagram of a thermal-neutron reactormade according to the teaching of FIGURE l, in which the circulation isaided by the centrifugal pumping effect of the rotary fuel discs.

FIGURE 10 is a fragmentary diagrammatic View of a thermal-neutronreactor turbine power plant according to the principle of FIGURE l,employing a gaseous working medium which is heated by contact with thefuel discs.

FIGURE 11 is a diagrammatic central cross section of a core assembly fora fast-neutron reactor according to the invention, the section beingtaken along its principal plane of symmetry, showing the overlappingsets of fuel discs.

FIGURE 12 is a diagrammatic central cross section of the FIGURE llstructure, the section being taken along the line 12-12 of FIGURE 11.

FIGURE 13 sketches the basic geometry of inner and outer core of thereactor illustrated in FIGURE ll in an idealized situation for Zeroshaft thickness.

FIGURE 14 shows the shading code used in FIGURES ll-15.

FIGURE l5 is a diagrammatic section showing typical fuel element andcoolant geometry within the inner core of the fast reactor of FIGURE ll.

FIGURE 16 gives qualitative curves for the temperature of a specificelement of a fuel disc of the fast reactor of FIGURE l1 as it rotates ata constant rate in a steady-state condition.

FIGURE l7 shows a qualitative curve of energy gain or loss of a specificsmall portion of a fuel disc of the fast reactor of lFIGURE 1l as itrotates at a constant rate in a steady-state condition.

FIGURE 18 gives qualitative curves for generated power, neutron flux,and temperature along the central line of the fuel assembly of the fastreactor of FIGURE ll in a steady-state condition.

FIGURE 19 is a diagrammatic flow diagram of a fastneutron reactoraccording to FIGURE l1, employing a liquid primary coolant, in whichcirculation is aided by the drag-pumping effect of the rotating fueldiscs.

FIGURE 20 is a diagrammatic flow diagram of a fastneutron reactoraccording to FIGURE 1l, employing a liquid primary coolant, in which thecirculation is supported by the centrifugal pumping eect of the rotatingfuel discs.

FIGURE 2l is a side view of a typical fuel disc as sembly with coolantow through the hollow shaft as employed in the suggested reactors ofboth FIGURE 9 and FIGURE 20.

FIGURE 22 is a fragmentary diagrammatic sectional view of a fast-neutronreactor turbine power plant according to the principles of the FIGURE llreactor, employing a gaseous working medium heated by contact with thefuel discs.

the power generated within the fuel.

FIGURE 23 sketches an internally cooled thermal reactor in which therotation of the fuel bearing disc assembly supports the circulation ofthe primary coolant by means of the centrifugal forces created.

FIGURE 24 is another View of the FIGURE 23 structure, showing itsappearance as viewed in section in the plane containing the axis ofrotation.

FIGURE 25 is a cross sectional detail of part of a rotary fuel assemblycontaining liquid fuel encased in a number of parallel discs mounted ona hollow shaft, in the static condition during filling, and FIGURE 26 isa similar view taken during rotation, after excess fuel in the shaft hasbeen drained olf, While the discs retain their filling under the inuenceof centrifugal forces.

FIGURE 27 depicts in diagrammatic section an internally cooled thermalreactor with rotary fuel assemblies containing liquid fuel, in which thefission products are continuously removed by centrifugal separationwithin the fuel assembly itself, during operation.

FIGURE 28 shows a reactor in which a body of liquid fuel is rotated bymeans of a rotary core vessel, with centrifugal separation of fissionproducts as in FIGURE 27, but without the use of a multi-disc fuelassembly.

In FIGURES l and 2 the shaft S carries-a number of circular fuel-bearingplates or discs P, which are interspersed by the moderator M in thereacting zone. Both cooling region C and reacting region Z are enclosedby the neutron reflector R, with suitable shaft seals for the fuelassembly shaft S or a canned motor or rotor arrangement.

An inner reflector R1 separates the reactingV zone and the cooling zoneand is provided with slots to permit rotation of the discs which formthe fuel assembly. The fuel proper is protected from corrosion and otherdamage by cladding, canning or other known means of support andcontainment. In case a powdered fuel material such as oxide, hydride,carbide, etc. is employed, the canning may -be limited to the outerfaces and rirn of the discs while the inner rim may remain partly openand lead into a cavity 1G11 within the shaft S through which gaseousfission products or their decay products such as xenonV 135 may beremoved. This open inner rim arrangement will also facilitate theintroduction and withdrawal of the powdered fuel into the discs, whileit offers freedom for thermal and other expansions occurring duringoperation. The powdered fuel will remain evenly compacted towards theouter rim throughout the disc under the influence of centrifugal forcesresulting from the rotation. v

The reacting zone covers an angle 9b as shown in FIG- URE 2, while thecooling regionmay cover the remainder of the arc minus the angleoccupied by the inner reflector R1. In the zone Z the space betweenneighboring discs is, except for small clearance, almost entirelyoccupied by moderator, as shown in FIGURE 4, while in the cooling zonethere is ample space for coolant flow as indicated in FIGURE 5. v

Starting from the center line X in FIGURE 2, we shall now follow a smallelement 102 of a fuel disc and describe the way in which temperature,neutron ux, and power generation vary in it asa function of angularposition 0, or, since the angular rate of rotation is assumed to beconstant, as a function of time.

Going in countercloclcwise direction, the selected element 1.02 movesaway from the center line X of the reacting zone. The neutron flux fallsoff gradually as does Since there is little circulation of coolantwithin this region, the temperature will continue to rise but at adecreasing rate, until the element emerges from the inner core Z intothe cooling region C. At that time the iiux falls off rapidly, remainingat aV very low value throughout the cooling zone, as Vdores the powergenerated. The temperature starts to decrease as soon as the -chosenelement is in contact with the coolant, and, once a steady-statecondition is reached, the total temperature drop in the cooling regionequals the total temperature rise in the reacting zone. Upon re-enteringthe inner core or reacting zone, the selected element of fuel 102 againexperiences increased neutron -ux and higher temperature. Theabove-described phenomena are indicated graphically in FIGURES 6 and 7.

FIGURE y8 shows how the rotation of the fuel discs P can be utilized asa main or auxiliary source of pumping power for circulating, by means oftangential drag, the primary coolant through its circuit. If necessary,additional pumping power may be provided -by using a pump 163 in theexternal circuit.

Alternately, as shown in FIGURE 9, this can be effected by utilizingcentrifugal forces set up by the disc rotation. The coolant in theFIGURE 9 structure is introduced through apertures 105 in the hollowshaft S, located between the individual fuel discs as shown in FIGURE2l.

In both the FIGURE 8 and FIGURE 9 arrangements the heat exchanger llt)transfers heat energy in the coolant to a secondary circuit.

The relatively wide space between the fuel discs in the cooling zoneavailable in my invention for the flow of coolant permits the use ofgaseous cooling Without much resistance to the gas ow. A suggestedapplication in an open cycle hot-air turbine power plant is indicated inFIGURE 10, in which the gas is compressed in compressor 166, heated inthe reactor, and then fed to turbine 1t7,vwherein the thermal energy inthe gas is partially converted to mechanical energy.

In the lfast reactor of FIGURES ll and l2, the fuel discs P1 and P2contain the appropriate amount of fissile material to sustain at thechosen physical and geometric conditions a fast-neutron chain reactionlargely restricted to' the zone of overlap Z, called the inner core. Inaddition, if the ire-actor is of the breeder type, the discs willcontain fertile material capable of being transformed into fissilematerial by neutron capture.

The fuel containing fissile and perhaps fertile material is suitablyprotected from damage by corrosion and other disruptive inuences by anysuitable means, such as cladding or canning. During operation atelevated temperatures the fuel may be in the liquid phase, keptdistributed uniformly within the disc walls by the centrifugal forces ofrotation.

Cooling of the fuel discs is achieved by contact with a liquid orgaseous coolant which circulates through the space between the reflectorwalls R. The cooling is mainly confined to the outer core zones C1 `andC2, although small amounts of coolant will How through the inner corezone Z, filling the clearances between adjoining fuel discs and carryingoif some excess heat. The reflector or blanket R surrounds the ent-iredual assembly las shown. A11 additional reflector R1 may enclose thereaction zone Z if desired, being slotted as shown in FIG- URE l1 toaccommodate the rotating fuel discs.

A fertile material may be incorporated in the reflectors or in thecoolant as well as in the fuel discs themselves. Rotation ofthe twofuel-disc assemblies can either be effected by leading fthe two shaftsS1 and S2 out of the core Vessel through a suitable coolant seal, or bya suitabile canned motor or rotor arrangement.

Nuclear control may 'be provided by control rods, positioned `forexample `at points B and C (FIGURE 13) or within the shafts S1 and S2,by variable retiector or blanket geometry, or by variable spacingbetween the fuel assembly shafts S1 and S2, which alters :the dimensionsof the inner core. An `additional control or adjustment of heat transferis provided by the choice of rotational rate of the fuel-discassemblies. At high rates of rotation the temperature range experiencedby the fuel discs will be reduced, and the `disruptive effects on thefuel discs of heatcyoling will be correspondingly reduced.

The coolant iiow may be directed opposite to the rotation of the fueldiscs in order to increase heat transfer efficiency, as indicated inFIGURE 12.

In FIGURE 13 it is shown that for the hypothetical case of zero shaftdiameter the maximum overlapping zone, which is the principal reactionzone, can encompass about 120 degrees of each set of discs. Forpr-actical dimensions of the shafts S1 and S2 the inner core region Zcan be considered as covering approximately one-third of the disc. As aresult of this, the cooling portion of each disc is roughly twice thelreacting portion and, therefore, for any selected element of la fueldisc, rotating at a constant rate, the heat-removal part of each cyclelasts twice as long the heat-generation phase. This tends to improve therate of heat removal to la considerable degree without necessitatinghigher fuel element temperatures.

As an example of possible dimensions of actual fast reactor fuelassemblies, FIGURE shows the geometry of part of the reacting zone for'a typical core. In the case illustrated the fuel layer F of 21/2millimeter thickness is enclosed between structural walls of 3Amillimeter, consisting 'of high temperature `and corrosion-resistantmaterial with a low absorption cross section for fast neutrons and ahigh mass number .to avoid moderation of the neutrons. The totalthickness of the individual discs is, therefore, 4 millimeters. If thesediscs lare mounted at lO millimeter intervals -between centers, thespace between them is 6 millimeters, and, therefore, in the overlappingzone the clearances between adjoining discs are 1 millimeter. Theaverage composition of the overlapping The large fractional value of theaspect area available for coolant ow will tend to reduce the powerconsumed for pumping the coolant through the primary circuit. Dependingon the physical, nuclear, yand chemical properties of the materialsactually employed in practice, these values may differ considerably fromthe exemplary ones illustrated.

The steady-state ldistribution of the lfast-reactor fuel elementtemperatures as 'a function of position around the axis is given invFIGURE 16 in arbitrary units. Since the fuel discs are rotating at aconstant rate, these curves are also typical for the temperature-timedependence for each element olf the fuel discs. The sawtooth curve showsa .rapid temperature rise over the principal reaction phase in the innercore 'followed by a less rapid cooling over a main cooling phase in theouter core which lasts approximately twice Ias long. As in the thermalreactor of FIG- URE 1, the temperature `amplitude will be reduced byrapid rotation, which also reduces the ill effects of heat cycling inthe fuel discs. Moreover, the overal-l thermal coupling between reactionand cooling zones is obviously higher in the case of high rotary speeds.

FIGURE 17 shows the energy balance of -an arbitrary element of a fueldisc of the FIGURE 11 fast reactor in a steady-state condition. Thetotalheat generation which occurs during passage through the principalreacting zone l in the inner |core is equal to the total heat yieldmainly confined yto the remainder of the cycle :and lastingapproximately twice as lonlg. The shaded areas in FIG- URE 17,indicating the integrated net heat balance within an element of 1a fueldisc, therefore, are o-f equal size under steady-state conditions.

FIGURE 18 indicates how in spite of concentration of virgin neutron uxand power generation in the main reacting zone, .the temperature isessentially spread out evenly over the entire fuel assembly of thefastreactor core. The curves present the temperature distribution as well-as `the magnitudes of power `generation and virgin neutron flux alongthe central line x-x of FIGURE l2.

High rotation speeds also offer the additional possibility of applyingthe kinetic energy imparted to the liquid coolant by the rotary discs,to the circulation of the coolant, although this goes at the expense ofcounterilux cooling. In other words, as with the FIGURE 1 reactor, it ispossible to utilize the drag forces between fuel discs and coolant tosupply part of the necessary power required for circulation of thecoolant through its circuit. A typical set-up of this nature is sketchedin FIGURE 19. In some cases the pump 103 may be eliminated when thefuel-disc drag furnishes sufficient power for the required rate ofcoolant circulation. The heat exchanger 110 transfers heat energy in thecoolant to a secondary circuit.

In FIGURE 2O I show that a combination of centrifugal and drag forcesmay be utilized to provide pumping power in the primary coolantcircuits. If the coolant is introduced into the core via hollow shaftsS1 and S2 through apertures 105 between the fuel discs (FIGURE 21), thespinning motion of these discs will create a radial ow component in thecoolant between the discs, thereby supplying motive power as requiredfor circulation of the coolant through the primary circuit comprisingthe core, the heat exchanger and the primary coolant pump 103.

The main cooling zones C1 and C2 of the FIGURE 11 reactor, with theirrelatively large effective aspect opening, allow free passage of largeamounts of coolant under a small pressure drop. Therefore, my invention,as previously mentioned with reference to FIGURE 10, is particularlysuited for application to high-power, gascooled reactors. FIGURE 22depicts a typical configuration whereby a fast reactor of the FIGURE 11type is utilized as a heat source in a gas turbine power plant withclosed or open cycle. The confinement of the greater portion of thecoolant gas to the zones C1 and C2 with relatively low neutron ux willhelp to reduce the neutroninduced radioactivity which, especially in thecase of an open air cycle, is particularly desirable. As in FIGURE 10,the compressor in FIGURE 22 is marked 106 and the turbine is marked 107.

Rotating fuel assemblies with self-pumping properties can, of course,also be used in reactors in which the coolant moves through the reactingpart of the core. FIGURES 23 and 24 show such an internally cooledreactor in which the rotation of the fuel assembly whirls the coolantthrough the clearances between fuel and moderator. A fuel assembly ofthe general nature of FIG- URE 21 may be employed in this case, althoughany shape of rotary symmetry will do. Whenever the coolant acts at thesame time as moderator, impellers may be provided between the fuel discsin order to improve the pumping efficiency. The coolant flow rate ishighest near the center shaft, where maximum neutron flux and heatgeneration exist, while near the perimeter of the fuel discs, wherepower generation is low, the coolant flow is slowed down as a result ofthe increasing ow area available.

When liquid fuel is employed, encased in hollow fuel discs, additionaladvantages can be realized by use of my invention. For example, thefilling and draining of the fuel discs may be facilitated by slightlytapering the inside walls of the cavities within the discs, as sketchedin FIGURES 25 and 26. Filling can be performed by raising the fuel levelin the shaft cavity during stand-still of the assembly (FIGURE 25). Oncethe assembly is rotating, the centrifugal forces will cause the fuel toow from the shaft cavity into the discs as shown in FIGURE 26. In thiscondition any considerable lowering of the rate of rotation will causepartial drainage of the fuel discs and resulting decrease of reactivity.This is an important safety feature.

A further important advantage of my invention when used with liquid fuelis that provision may be made for draining olf during operation thecentermost layer of liquid fuel, at intervals or continuously, in orderto remove fission products which have accumulated there as a result ofcentrifugal segregation. Thus, without the disadvantage of extra fuelholdup in reprocessing loops, continuous centrifugal purification isobtained, permitting a higher burn-up rate and increasing inherentsafety by reducing the excess reactivity required to compensate forfission-product poisoning. In FIGURE 27 a simple arrangement is shown asan example of continuous removal of fission products by means of myinvention. In that structure, liquid fuel is circulated through a narrowannular cavity C in the shaft S, the cavity 112 being in Comunicationwith the interiors of all the fuel discs. During operation of thereactor, the lighter fission-product atoms, as they are formed in thefuel, tend to work to the central parts of the discs, where they arepicked up by the circulating current of liquid fuel in the cavity 112and are carried out of the reactor, to be replaced by the heavy atoms offuel and fertile material pumped into cavity 112.

FIGURE 28 shows how the liquid fuel can be rotated by means of a rotarycore vessel to achieve continuous centrifugal separation of fissionproducts from the fuel. This structure does not have a multi-disc shape,the actual fuel assembly being entirely a liquid rotary body of fuel,confined within the rotating cylindrical fuel housing 115.

While I have in this specification described and illus;

trated my invention in a number of embodiments, it is to be understoodthat they are merely exemplary, and that persons skilled in the art willbe able to make many changes and variations in the structures shownwithout departing from the principles and spirit of my invention.Accordingly, the scope of my invention should be primarily determinedfrom the appended claims.

I claim:

l. In a nuclear reactor the combination comprising a core containing aplurality of disc-shaped, fuel-containing elements, said elements beingmounted for rotation about their respective centers in a plurality ofspaced parallel planes, means for rotating said elements, means forcreating a condition of criticality in said plurality of discs oversegments of said discs, said segments progressing around said discsduring rotation thereof, coolant means surrounding each of said discsincluding said critical segments, and means for passing said coolantmeans around said discs in a direction parallel to the plane of rotationof said discs with the coolant flow rate highest adjacent the center ofrotation of said discs.

2. The reactor of claim l wherein said plurality of fuel discs aremounted for rotation about a common axis and said means for creating acondition of criticality includes a neutron moderator adjacent each ofsaid discs throughout said critical segment of each of said discs.

3. The reactor of claim l wherein said plurality of fuel discs aremounted for rotation about a plurality of parallel axes, and whereinsaid means for creating a condition of criticality includes theoverlapping of a portion of the discs of each of the plurality of aXesso that criticality is attained only in the overlapping segments of saiddiscs.

4. The nuclear reactor of claim l wherein said discshaped elements arehollow, wherein said fuel is a fluid containing ssionable material, andwherein means, communicating with the interior of said hollow elements,is provided for passing said fluid fuel into and out of said disc-shapedelements.

5. The nuclear reactor of claim 1 wherein said discshaped fuel elementscomprise a solid ssionable material fuel core and cladding enclosingsaid fuel core, and including a neutron reector disposed about thecritical segment of said discs.

References Cited in the tile of this patent UNITED STATES PATENTS2,812,304 Wheeler NOV. 5, 1957

1. IN A NUCLEAR REACTOR THE COMBINATION COMPRISING A CORE CONTAINING APLURALITY OF DISC-SHAPED, FUEL-CONTAINING ELEMENTS, SAID ELEMENTS BEINGNOUNTED FOR ROTATION ABOUT THEIR RESPECTIVE CENTERS IN A PLURALITY OFSPACED PARALLEL PLANES, MEANS FOR ROTATING SAID ELEMENTS, MEANS FORCREATING A CONDITION OF CRITICALLY IN SUCH PLURALITY OF DISCS OVERSEGMENTS OF SAID DISC, SAID SEGMENT PROGESSING ARTOUND SAID DISCS DURINGROTATION THEREOF, COOLANT MEANS SURROUNDING EACH OF SAID DISCS INCLUDINGSAID CRITICAL SEGMENTS, AND MEANS FOR PASSONF SAID COOLANT MEANS AROUNDSAID DISCS IN A DIRECTION PARALLEL TO THE PLANE OF ROTATION OF SAIDDISCS WITH THE COOLANT FLOW RATE HIGHEST ADJACENT THE CENTER OF ROTATIONOF SAID DISCS.